VagrantDestroyUp works properly now.

Because VagrantDestroyUp made two async calls, one for 'vagrant destroy' and one for 'vagrant up', these calls didn't always happen in the same order and often happened simultaneously.

Using the old code for invoking vagrant commands, we force a synchronous invocation of 'vagrant destroy' and then do 'vagrant up' asynchronously since it takes far longer to execute.
Since the command says 'destroy && up', I also added in some logic to only have the up command happen if the destroy succeeded successfully.
Merge pull request #4 from NaleagDeco/delete-up

Delete && Up didn't work properly, the destroy was issued asynchronously so was sometimes being issued after the up.

destroy is now synchronous, and it's exit status is checked before executing the up command.
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Added a contributors section.
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